I can't modify a feature

There are certain features that can't be modified:

Country, state, and district borders.
Google Maps relies primarily on high quality, neutral third-party data sources for country borders. We’ve locked country borders to anyone outside the Google Map Maker product team. We ensure that only third-party data sources are being used in abidance with international conventions.

Disputed features.
These features are determined on a case-by-case basis, with an eye towards avoiding the back-and-forth editing of particularly controversial, contentious areas. As Map Maker follows the "last approved edit wins" model, the most effective, neutral decision is to prevent editing altogether. Read more to learn how Google approaches a similar type of issue.

Pending attributes/geometry.
Any pending feature will lock only the attribute/geometry under review. However, other attributes associated with the same feature or any of the connecting features will still be editable.

Countries not open for Map Maker.
There are still many regions that are not yet open for editing in Map Maker. While we work on opening up Map Maker for the rest of the world, we keep this list of regions open for editing up-to-date.

Large polygons and water bodies.
Some polygons and most bodies of water are uneditable in Map Maker. If you notice an incorrect uneditable polygon, you can correct inaccuracies by creating duplicate polygons. Make sure that the new duplicate shape is accurate and detailed.